Effect of nickel hydroxde injections on the mass transfer of corrosion products in high temperature, high pressure water circuits

Following reports that injections of nickel hydroxide facilitated the removal of crud from the Garigliano Boiling Water Reactor (BWR), nickel hydroxide was injected into a high temperature water loop simulating BWR operation. The injections repeatedly caused large crud bursts in which iron appeared almost exclusively as nickel ferrite. After the crud bursts, iron and nickel redeposited rapidly and preferentially into heated surfaces, although the mobility of ferritic crud in the loop was increased. Filtration and ion exchange of the coolant, accompanied by the continuous injection of nickel hydroxide, removed small quantities of ferritic crud from the system, but not from heated surfaces. Less than 2% of the nickel injected was removed from the loop. The injection of small quantities of nickel during shutdown did not increase the rate of removal of iron by the purification system, although 75% of the nickel injected was eventually removed by the purification system. Given the tendency of nickel to remain in the system and deposit on heated surfaces, it is probable that injection of nickel into the primary coolant of a BWR would lead to increased radiation fields around the plant, even though small quantities of ferritic crud may be removed from the system. The increased mobility of nickel ferrite is worthy of further investigation, but at present the injection of nickel into BWRs cannot be recommended